Thank you AmbientLight for your kind advice. I think you are right about FF since I was having a lot of trouble with the 7D obtaining focus and also keeping the whole bird in the frame. One day I hope to upgrade to the 5D3 or something similar in the future.

What lens are you using? I use a 70-300L with a 7D for birds in flight and would just use less zoom than buy a new full frame body. The auto focus of the 7D is more than adequate for sharp birds in flight when used with a fast enough shutter speed. If birds are flying laterally, it's hard to get a high percentage of keepers, but with the 7D's frames/second, you should get some. Do you use back button focus in servo? That change helped my "keep" rate a lot.

Hi CT John,

I started out using my 100-400L but I was usually shooting in the late afternoon and often it is overcast and cloudy then. The light was not bright and so I had low shutter speed and large apertures to keep ISO <800. The focus and IS on the 100-400 was not great. So I started using my recently purchased 70-200L f/2.8 ii for the f/2.8 focusing speed. I also was often too high on the focal range on the 400mm and the 200mm made me not zoom in so much which helped like you suggested. I have never tried back button focus (I'm an old guy who is very timid or slow to try new things) but I know I should learn that technique. Also, I need to practice panning skills. The heron was flying both laterally and towards me at the same time. I was using AI servo, expanded or manual select center zone AF, high speed continuous shutter, and AI Servo tracking sensitivity on "slow". Are those the correct settings to use? Thanks everyone for any advice.

Those settings look fine - I use auto select for auto focus most of the time, and my Servo tracking sensitivity on normal....not sure it that makes a lot of difference. I would recommend trying back button focusing because I think it's easier to keep that depressed while panning rather than half depressing the shutter release button.

AI Servo tracking on slow or "1" does make a difference. It enables the AF system to track the bird more efficiently and to ignore things that may pop into view or slight alterations in course. Auto select for BIF usually results in less keepers with my findings after 3 years with my 7D. Back button focus is excellent as I've suggested previously.

Also, I've found that once I MFA'd my 100-400mm the sharpness and accuracy went through the roof! Have you MFA'd you're lenses yet Serendipity? It made mine like getting a brand new lens for about an hours worth of work...

Thanks again Ken for all your excellent advice. I haven't AFMA any lens yet (I don't know how, but I will buy that Focal software I read about on CR and try it). I did send my 7D and 100-400L from HI to CA Canon Service center about a year ago for them to calibrate. When I got it back, it did seem a little sharper. Also, I need to set up my camera and try back button focus. I have been using my recently purchased 70-200L f/2.8ii for BIF since it can capture focus using the f/2.8 and also not so tele since the herons are close (fly between my house and the neighbors house).